Distribution and Diffusion Behaviors of Perfluorinated Compounds with Low Pressure Reverse Osmosis Membranes

Low pressure reverse osmosis (LPRO) membrane filtration has emerged as the best alternative to ordinary reverse osmosis (RO) membrane filtration due to very low operating pressure involved with the former resulting in low cost. However, behaviors of perfluorinated compounds (PFCs) with LPRO membrane filtration are not known since the compounds as water/wastewater contaminants have only a very short history. Therefore, adsorption and diffusion behaviors of selected perfluoroalkyl carboxylate (PFAC) and perfluoroalkyl sulfonate (PFAS) compounds with a tight and a loose LPRO membranes were tested in laboratory experiments. Distribution coefficient (logKmw) and diffusion coefficient (Dp) values for the compounds were experimentally determined for the first time. The Dp values were about three orders of magnitude larger than those for pharmaceutical and endocrine disrupting compounds. The compounds exhibited similar behaviors to those of pharmaceutical and endocrine disrupting chemicals reported earlier. Adsorption of PFCs to membranes was directly correlated to molecular weight (MW) and carbon-chain length, while their diffusion through membrane pores showed inverse correlations with the parameters. Similarly, their rejections were directly correlated to their logKmw values and MW. However, significance of carbon-chain length on diffusion was not well understood, and hence further investigations should be devoted to elucidate on the point.